The present invention relates to inductive components and methods for manufacturing these components.
Inductive components are commonly fabricated using ferromagnetic cores and windings of insulated electrical wire. The ferromagnetic cores are typically toroidal cores, rod cores, or assemblies made of a lower E shaped ferromagnetic part and a ferromagnetic cap connecting the three legs of the E such as shown in FIG. 1.
The toroid and rod cores are manually or automatically wound with the insulated copper wire to form a number of multiple turn windings for a transformer or a single winding for an inductor. The assembly is then typically encapsulated to protect the wires. The circuit connection is made by the solder termination of the wires as required by the application. This approach has high labor costs because of individual part handling. It has large variability in electronic parameters such as leakage inductance, distributed and interwinding capacitance, and common mode imbalance between windings because of the difficulty in exact placement of the copper wires.
The E shaped and encompassing cap assembly of FIG. 1 is made into an inductive component by manually or automatically winding copper insulated wires around the legs of the E as required. Either gluing or clamping the cap in place and final encapsulation completes this subassembly. Similarly, the circuit connection is made by means of solder termination of the wires as required by the application. Not only does this device have the limitations of the toroid and rod core, as mentioned above, but also it generally is a much larger device. Because the cap is a separate device the magnetic paths have a resistance of non-ferromagnetic gaps between the E and the cap reducing the efficiency of the transformer.
Power transformers constructed as shown in FIG. 1 have the further disadvantage that the heat resulting from the resistance losses in the windings is not easily dissipated because the E core and cap isolate these windings from a heat sink.
The preferred embodiments of the present invention provide inductors and transformers and methods of manufacturing these devices which offer very significant advantages over the state-of-the-art. These inductors and transformers connected in accordance with this invention have a number of applications in the electronics, telecommunication and computer fields. In one preferred embodiment described below, a rectangular slab of ferromagnetic material is encapsulated between printed circuitry. A plurality of through holes (vias) are drilled through or formed during manufacture of the slab from the top face of the slab to the bottom face of the slab, the number of holes corresponding to the number of desired turns of the windings. This embodiment utilizes Ampere""s Law in a very novel manner to form a transformer, inductor, or the like within the circuit board rather than the use or assembly of discrete inductive devices to the circuit board. Thus, the windings are not insulated electric wires. Rather, the holes through the slab are made electrically conductive by through hole plating or the like and electrically connect with the printed circuits encapsulating the slab. This pattern of plated through holes and the printed circuitry form the inductor and transformer windings with the core of the inductors and transformers being the drilled or formed slab of ferromagnetic material. This embodiment provides substantial improvements, particularly in fabricating high frequency inductors and transformers.
In another preferred embodiment described below, the core of the inductors or transformers comprises cores formed by a multi-layer series of thin concentric ferromagnetic metal rings supported on a suitable substrate such as a flex circuit (FLEX) or printed circuit board (PCB). Through holes proximate these concentric ring cores provide electrical connection with printed circuitry to provide the inductor and transformer windings. This embodiment enables construction of high permeability inductors and transformers having minimal eddy current effects. Inductors and transformers so constructed have particular application for miniature low frequency power supplies.
In addition to the advantages described above, the preferred embodiments have a number of additional significant advantages. These include: superior heat removal, outside connections that are more accessible to simplify electrical connection, shorter flux paths to increase magnetic performance, simpler fabrication, interconnections that are more integrated, smaller inductive devices, superior performance, and excellent manufacturing repeatability.